An existing power line network belongs to a shared network, and a shared medium is an electric wave transmitted on a power line. Power line communication is in a bus type, and cannot enable irrelevant sites to be separated from each other as an Ethernet line does; therefore, in a case in which attenuation is not considered, the electric wave transmitted on the power line may be received by all sites on the power line. Using the power line network as an example for illustration, a structure of the power line network is shown in FIG. 1. A central coordinator (CCO) is a concentrator on a transformer, and the other sites are meters. The CCO and the meters are connected through the power line. In an actual application, several transformers are generally integrated in one place, each transformer is provided with one CCO module, a CCO module and a site (meter) belonging to the CCO module form a power line network, and multiple transformers and corresponding sites form multiple power line networks. An example of FIG. 2 indicates a scenario in which multiple power line networks included by three transformers coexist. In this example, three transformers are connected to one bus. Therefore, three power line networks to which the three transformers belong are adjacent networks.
In a shared network, a signal interference problem exists when communication is performed between sites. If two sites emit signals synchronously, the emitted signals interfere with each other, thereby leading to a communication failure. Alternatively, electromagnetic interference outside the sites in the network also causes signal interference.
In addition, a signal attenuation problem also exists in communication between sites. If two sites are far away from each other or have serious interference, a signal emitted by one site will be seriously distorted when transferred to another site, and cannot be identified.
In order to resolve the problems of signal interference and attenuation in the shared network, the prior art provides the following two solutions, which specifically include:
Solution 1 of the Prior Art: A Frequency Division Solution
Total bandwidth used for a transmission channel is divided into several frequency sub-bands, each frequency sub-band may be used as an independent transmission channel, and each network corresponds to a frequency sub-band. However, in a power line environment, there are not many available frequency bands, and in most shared networks, only one kind of frequency bands can be used. Therefore, in this solution, a frequency band is divided into multiple frequency sub-bands; as a result, the bandwidth utilization is lowered.
Solution 2 of the Prior Art: A Time Division Solution
Time division is performed on a transmission path, each timeslot can be used by only one network, and multiple networks alternately use different timeslots (for example, in a first timeslot allocation period, a network 1 uses a timeslot 1, a network 2 correspondingly uses a timeslot 2, and then a network 3 correspondingly uses a timeslot 3; and the subsequent period timeslot allocation rule is the same as that of the timeslot allocation period). Refer to FIG. 3 for details. Defects of the solution are that: in the power line network, multiple networks generally interwork at a root node, and most sub-nodes in the network can only communicate with nodes in a network to which the sub-nodes belong. Because each network exclusively occupies a timeslot, the utilization of the network bandwidth decreases by times, and a service delay is increased. Therefore, existing application requirements cannot be satisfied.